https://bugs.freedesktop.org/show_bug.cgi?id=35460

--- Comment #17 from Chris Wilson chris@chris-wilson.co.uk 2011-12-09 07:25:13 PST --- No, we don't buffer cursors. A single cursor bo is updated every time its image changes. (Whilst possible, I don't it is an interesting optimisation to cache the bo for a variety of cursors.)

This could just be a bad bit of RAM, bad cache, or signs of incoherency... Can you retry Daniel's original overkill patch and see if this corruption ever turns up? Though I think we can safely say that the current mb is an improvement.